It is proposed to investigate the uvrA, uvrB, and uvrC enzymes of E.coli which incise DNA irradiated with ultraviolet light. An obstacle to the study of these enzymes has been the small yields normally obtained and the difficulty of getting sufficient material for study. To overcome this, it is proposed to make use of three recently isolated lambda transducing phages which carry these genes. Genetic and enzymatic methods will be used to develop these phages to increase the enzyme yields. The uvrA, and uvrB, and uvrC proteins will then be assayed by complementation in the corresponding mutants, and purified if sufficient activity is obtained. We will next investigate the role of the three components in the incision of DNA containing pyrimidine dimers or interstrand crosslinks. If sufficient DNA containing incised crosslinks can be prepared, it will be used as a substrate for initiating recombination in an in vitro system for studying the enzymes of genetic recombination.